A mixed signal integrated circuit has both analog circuits and digital circuits on a single semiconductor die. Examples of mixed signal integrated circuits include data converters using delta-sigma modulation, analog-to-digital converters, digital-to-analog converters, digital radio chips, and digitally controlled sound chips.
Because of the use of both digital signal processing and analog circuitry, mixed signal integrated circuits are usually designed for a very specific purpose and their design requires a high level of expertise and careful use of Computer Aided Design (CAD) tools. Automated testing of the finished chips can be challenging.
There are a number of design challenges associated with mixed signal integrated circuits. For example, CMOS technology is usually optimal for digital performance and scaling while bipolar transistors are usually optimal for analog performance, yet until recently it has been difficult to either combine these cost-effectively or to design both analog and digital circuits in a single technology without serious performance trade-offs. The advent of technologies like high performance CMOS, BiCMOS, CMOS SOI and SiGe has removed many of these trade-offs, thereby presenting new opportunities for mixed signal circuits.
Still, problems remain. For example, testing the functional operation of mixed-signal integrated circuits remains complex, expensive and often a “one-off” implementation task. In addition, systematic design methodologies comparable to digital design methods are far more primitive in the analog and mixed signal arena. Analog circuit design cannot be automated to the same extent as digital circuit design. Combining the two technologies multiplies automation complication.
Mixed signal circuits with fixed function analog cells are known. The fixed function analog cells may have programmable interconnect to implement various analog operations. Unfortunately, such designs have limited flexibility and consume relatively large amounts of chip space. Accordingly, it would be desirable to provide an improved mixed signal circuit.